Tunneling vision

Age-related macular degeneration involves loss of vision in the center of the visual field known as the macula, an oval-shaped, highly-pigmented yellow region near the center of the retina at the back of the human eye.

This is the part of the eye where vision-producing cells (rods and cones) are most densely packed and eyesight most acute.

The primary consequence of AMD is a sort of central blindness, making it difficult to read or recognize faces, though enough peripheral vision may remain to allow for other activities in life. There are two forms of AMD: “dry” and “wet.”

The dry form is most common, about 90 percent of cases. It happens when light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye. As dry AMD progresses, sufferers may see a blurred spot in the center of their vision, a phenomenon known as “geographic atrophy.” Over time, central vision increasingly diminishes as less and less of the macula works properly.

The wet form is more severe, at least compared to the early and intermediate stages of dry AMD. It occurs when abnormal blood vessels behind the retina start to grow under the macula. These vessels can be fragile and leak blood and fluid. The blood and fluid cause the macula to swell, rapidly damaging the retina. Central vision loss happens more quickly.

As the name suggests, AMD is a consequence of aging. It most often occurs after the age of 50. Age is the greatest risk factor, but smoking, race and family history play a part. A healthy lifestyle – good diet, exercise – appears to reduce the odds.

Much remains unknown about AMD, particularly at the molecular and cellular level. In a new paper, published in the Proceedings of the Academy of National Sciences, Kang Zhang, MD, PhD, of UC San Diego’s Institute of Genomic Medicine and Shiley Eye Center, and colleagues describe some of the challenges still facing researchers, reporting that AMD risk is impacted by how a particular protein called complement factor H influences oxidative stress,inflammation and abnormal angiogenesis in the eye.

In the scanning electron micrograph above, from Joseph Lust at the University of Rochester, part of the inner eye is revealed densely packed ganglion cells (false-colored green) are neurons that take visual information collected by the retina and transmit it to the brain. Photoreceptor rod cells, primarily used in night vision, are colored blue. Retinal pigmented epithelium is colored orange. This single layer of pigmented cells shields the retina from excessive incoming light.

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(Source: ucsdhealthsciences)